Condensation Nucleus Counter Research Articles

Effect of disk rotational speed on contamination particles generated in a hard disk drive

In high-density hard disk drives, the slider should be made to fly close to the magnetic recording disk to generate better signal resolution and at an increasingly high velocity to achieve better data rate. The slider disk interaction in CSS (contact-start-stop) mode is an important source of particle generation. Contamination particles in the hard disk drive can cause serious problems including slider crash and thermal asperities. We investigated the number and the sizes of particles generated in the hard disk drive, operating at increasing disk rotational speeds, in the CSS mode. Condensation nucleus counter (CNC) and PSS (particle size selector) were used for this investigation. In addition, we examined the particle components by using SEM (scanning electron microscopes), AES (auger electron spectroscopy) and TOF-SIMS (time of flight-secondary ions mass spectrometry). The increasing disk rotational speed directly affected the particle generation by slider disk interaction. The number of particles that were generated increased with the disk rotational speed. The particle generation rate increased rapidly at motor speeds above 8000 rpm. This increase may be due to the increased slider disk interaction. Particle sizes ranged from 14 to 200 nm. The particles generated by slider disk interaction came from the lubricant on the disk, coating layer of the disk, and also slider surface.

Airborne bacteria as cloud condensation nuclei

Bacteria cultivated from aerosol and cloud water samples collected at a remote Austrian mountain site under wintry conditions were tested for their ability to act as cloud condensation nuclei (CCN). The experiment was carried out with a cloud condensation nuclei counter (CCNC) operating on the principle of a static thermal diffusion chamber. Average concentrations of cultivable airborne bacteria amounted to 8 colony forming units (CFU) m−3 in aerosol samples and to 79 CFU mL−1 in cloud water. The set of tested bacteria comprised Gram positive and Gram negative but no known ice nucleating species. At supersaturations between 0.07 and 0.11% all types of bacteria were activated as CCN. As the sizes of the bacteria were smaller than the Kelvin diameters for the respective supersaturations, the physico‐chemical properties of their outer cell walls must have enhanced their CCN activity.

Formation of cloud droplets by multicomponent organic particles

Cloud condensation nuclei (CCN) in the atmosphere are usually composed of multiple inorganic and organic chemical species. Determining the ability of these multicomponent particles to activate into cloud droplets is necessary for understanding and quantifying the effect of aerosols on cloud formation and properties. Internally mixed, multicomponent particles as well as particles consisting of a core coated with hexadecane were used in the present study. Laboratory experiments were performed using combinations of sodium chloride, ammonium sulfate, pinonic acid, pinic acid, norpinic acid, glutamic acid, leucine, and hexadecane. Activation diameters were determined combining a Tandem Differential Mobility Analyzer (TDMA) with a thermal diffusion Cloud Condensation Nucleus Counter (CCNC). Studies were performed at supersaturations of 0.3% and 1% with dry particle diameters ranging between 0.02 and 0.2 micrometers. The results were compared to a theory assuming additive behavior of the constituent species. This assumption was sufficient for the prediction of the CCN activation diameter of the mixed particles.

Correlations for Vapor Nucleating Critical Embryo Parameters

Condensation nucleation light scattering detection in principle works by converting the effluent of the chromatographic separation into an aerosol and then selectively evaporating the mobile phase, leaving less volatile analytes and nonvolatile impurities as dry aerosol particles. The dry particles produced are then exposed to an environment that is saturated with the vapors of an organic solvent (commonly n-butanol). The blend of aerosol particles and organic vapor is then cooled so that conditions of vapor supersaturation are achieved. In principle, the vapor then condenses onto the dry particles, growing each particle (ideally) from as small as a few nanometers in diameter into a droplet with a diameter up to about 10 μm. The grown droplets are then passed through a beam of light, and the light scattered by the droplets is detected and used as the detector response. This growth and detection step is generally carried out using commercial continuous-flow condensation nucleus counters. In the present research, the possibility of using other fluids than the commonly used n-butanol is investigated. The Kelvin equation and the Nucleation theorem [Anisimov et al. (1978)] are used to evaluate a range of fluids for efficacy of growing small particles by condensation nucleation. Using the available experimental data on vapor nucleation, the correlations of Kelvin diameters (the critical embryo sizes) and the bulk surface tension with dielectric constants of working liquids are found. A simple method for choosing the most efficient fluid, within a class of fluids, for growth of small particles is suggested.

Measurement of cluster ions and residue nanoparticles from water samples with an electrospray/differential mobility analyzer.

Cluster ions and residue nanoparticles with sizes below 30 nm were generated by electrospraying (ES) and drying droplets of pure water, tap water, and aqueous solutions of salts. The mobility spectra of the cluster ions between 9.1 and 9.3 x 10(-5) m2/(V s) were measured using a differential mobility analyzer (DMA) operated at room temperature and atmospheric pressure. A modified Faraday cup and a condensation nucleus counter were used for detection. The concentrations of total residue/contaminants in the water were determined as a function of sizes of measured aerosol particles and of the initial droplets. Method detection limits were at sub-ppb level for pure water and sub-ppm level for tap water. ES/DMA is capable of simultaneously measuring the mobility distribution of cluster ions and concentration of total residue present in water samples.

Brownian coagulation of polydisperse aerosols in the transition regime

Brownian coagulation of aerosols in the transition regime was studied at Knudsen numbers ranging from 0.8 to 5.5. Coagulation rates were obtained from the change in total number concentration of polydisperse oleic acid and the sodium chloride aerosols with geometric mean diameters between 25 and 150 nm in a closed chamber at atmospheric pressure. Particle size distributions and concentrations were measured by scanning mobility particle sizer (TSI) and condensation nuclei counter (TSI), respectively. The experimental coagulation rates took deposition rates (diffusional wall loss rates) into account, because coagulation and diffusion deposition occur simultaneously in a closed chamber. In addition, to obtain the accurate coagulation rates of the experiments, two approaches were used and compared with each other. The experimental results were observed to follow the theoretical results of Dahneke and Fuchs, which showed that coagulation coefficients increased just a little in the transition regime.

Nanoparticle Formation Mechanism in CVD Reactor with Ionization of Source Vapor

A new chemical vapor deposition (CVD) method, called ionization CVD, was developed, to produce non-agglomerated nanoparticles in which reactant gases are charged. A sonic-jet corona discharger was used as an ionizer in the developed nanoparticle generator. For a tetraethylorthosilicate (TEOS)/O2 chemical system, SiO2 nanoparticles were prepared. All particles formed by the ionization CVD were charged unipolarly. SEM micrographs of particles showed that the repulsive Coulombic force between charged particles reduces their coagulation rate and produces non-agglomerated nanoparticles that have a relatively high number concentration and small size. An external field was used to collect the charged particles onto Si wafers. These collected samples indicated that the deposition of charged particles could be controlled by the external electric field. Particle concentration measurement with a condensation nucleus counter at various TEOS concentrations suggested the particle formation mechanism in the ionization CVD was an ion-induced nucleation.

Cloud activation of single‐component organic aerosol particles

The organic fraction of ambient aerosols is a complex mixture of hundreds of organic compounds varying in chemical structure and physical properties. The cloud condensation nuclei (CCN) activities of single‐component organic particles were experimentally investigated. Activation diameters were determined using a Tandem Differential Mobility Analyzer and a thermal diffusion Cloud Condensation Nucleus Counter. Studies were performed at supersaturations of 0.3 and 1% with dry particle diameters ranging between 0.02 and 0.2 μm. The focus was on both hygroscopic secondary organics and hydrophobic primary organics. Laboratory experiments were performed with sodium chloride, ammonium sulfate, glutaric acid, adipic acid, pinonic acid, glutamic acid, leucine, cholesterol, pinic acid, norpinic acid, hexadecane, hexadecanol, myristic acid, palmitic acid, and stearic acid. The results were compared with the classical Köhler theory and a theory that accounts for the limited solubility of many organics. It was discovered that organic species with bulk solubilities in water less than 0.01 g cm−3 can be a good source of CCN in the atmosphere if their contact angles with water are zero. Experiments confirmed that Köhler theory works well in predicting activation of soluble inorganic species and organics that are wettable by water, while an extension of the theory appears necessary to account for the low‐solubility organic species that are not wettable by water.

CCN activation of oxalic and malonic acid test aerosols with the University of Vienna cloud condensation nuclei counter

The cloud droplet activation of monodisperse laboratory aerosols consisting of single organic and inorganic substances as well as a mixture of several substances was investigated using the University of Vienna cloud condensation nuclei counter (CCNC). The CCNC operates on the principle of a static thermal diffusion chamber. Water vapour supersaturations can be set in the range from 0.1% to 2%. Aqueous solutions of oxalic acid and malonic acid as well as solutions of inorganic compounds (NaCl and (NH 4) 2SO 4) were nebulized in a Collison atomizer and then passed through a closed-loop differential mobility particle spectrometer to produce monodispersed particles. An internally mixed aerosol consisting of ammonium sulphate, oxalic acid and malonic acid with relative concentrations resembling those found in cloud water at a mountain station [Löflund, Kasper-Giebl, Schuster, Giebl, Hitzenberger, Reischl et al. (2002) Atmos. Environ. 36, 1553] was also investigated for cloud condensation nuclei (CCN) activation. All these particles were activated at supersaturations expected from Köhler theory. Oxalic and malonic acid particles are therefore expected to be good atmospheric CCN both as pure particles and as internally mixed particles containing other chemical compounds.

Performance of a mixing-type CNC for nanoparticles at low-pressure conditions

A mixing-type condensation nucleus counter (MTCNC) was used to detect nanometer-sized particles suspended under low-pressure conditions. The experimental results show that MTCNC is capable of measuring nanoparticles smaller than 10 nm at low pressures above 65 Torr (8.644 kPa) by adjusting the rate of the aerosol flow, the amount of vapor and temperature depending on the desired operation pressure. At pressures above 160 Torr (21.33 kPa) , the optimal operation conditions of a MTCNC, variables such as the saturator temperature, condenser temperature and mixing ratio are similar to those used at atmospheric pressure. Since the condensational growth of particles depends greatly upon the residence time, the current MTCNC needs improvement to increase the growth time under even lower pressure conditions. At the optimal operation conditions, the counting efficiencies for nanoparticle size 3 nm particles are 85% at atmospheric pressure and 40% at an operating pressure of 115 Torr (15.33 kPa) , respectively.

Fast Mixing Condensation Nucleus Counter: Application to Rapid Scanning Differential Mobility Analyzer Measurements

Condensation nucleus counters (CNCs) exhibit slower time response than expected due to mixing effects within the detector.This mixing produces an exponential distribution of delay times with a characteristic mixing time m that ranges from 0.1 s to 0.9 s for commonly used instruments and limits their usefulness for measuring rapidly changing aerosols. Moreover, when used as detectors in the scanning electrical mobility spectrometer (SEMS; also known as scanning mobility particle sizer, SMPS), CNCs limit the speed with which size distribution measurements can be made. In order to overcome this limitation, a new, fast-response mixing CNC (MCNC) has been developed and characterized. The time response of this new detector and TSI Models 3025 and 3010 CNCs has been measured using a spark source to generate an aerosol pulse. The mixing induced response smearing of this new detector, m , of this instrument is 0.058 s, which is significantly shorter than either of the other instruments tested. Its lower detection limit is about 5 nm diameter. The high aerosol flow rate of the MCNC (0.65 l min -1 ), fast time response, and low detection limit make it an ideal detector for SEMS/SMPS measurements. Using this MCNC as a detector for the SEMS, size distribution measurements over the 5 nm to 140 nm range have been made in 3 s with minimal distortion. The size distribution of a coagulation aerosol was effectively recovered by deconvolution with scans as short as 1 s. Uncertainties in the 1 s scans result, in part, from electronics problems in the scanning DMA.

Sizing Small Sulfuric Acid Particles with an Ultrafine Particle Condensation Nucleus Counter

The sizing capability of an ultrafine particle condensation nucleus counter (which uses butanol as the condensing fluid) equipped with pulse height analysis was evaluated in terms of particle composition for sulfuric acid aerosol and sulfuric acid aerosol to which gas-phase ammonia had been added. The response of the counter depended on composition for a range of particle sizes when the water partial pressure was low. For water partial pressures 4 nm in diameter, the response (pulse heights) of the instrument to particles of a given size was substantially different for sulfuric acid particles and those that were neutralized with ammonia. For water partial pressures > 5 Torr, however, neutralizing the particles with ammonia had little effect on pulse height distributions. For particles smaller than 4 nm diameter the pulse heights were insensitive to exposure to ammonia.

Collection efficiency of sintered ceramic filters made of submicron spheres

The performance of filters made of sintered submicron alumina particles was evaluated. The filter has a high collection efficiency and high pressure drop, requiring the development of a special measuring system for its evaluation. The system consists of a polydisperse NaCl particle generator, a differential mobility analyzer (DMA), an ejector to supply aerosols for testing filters with high pressure drop, and a mixing-type condensation nucleus counter (CNC) capable of obtaining a stable reading of very low concentration particles. Penetrations as low as 10 −9 can be measured in the particle diameter range of 0.02–0.14 μm. Two filters made by sintering 0.60 and 0.84 μm alumina particles were evaluated. The experimental data collected served as the basis of theoretical development. Following the single fibre theory, the filter penetration is calculated by using a single sphere as the element. Both the diffusion and interception collection mechanisms were taken into account. The resulting equation gives a general trend of efficiency curves as a function of the parameters involved, e.g. the test aerosol size, packed particle size and filtration velocity. However, it is not sufficiently accurate for providing quantitative performance results.

Nolan–Pollak type CN counters in the Vienna aerosol workshop

Three “standard” Nolan–Pollak (N–P) and a modified N–P design condensation nucleus (CN) counters were included in the Vienna Workshop on Intercomparison of Condensation Nuclei and Aerosol Particle counters. These counters came from diverse backgrounds, namely programs in USA, Europe and Australia. In this work, principles of the operation and previous history of calibration of the N–P expansion counter are briefly reviewed and comparisons between the particular counters used in the workshop are presented and discussed. Counting agreement was found to be very good between the N–P counters, typically better than ±12% for a range of aerosol sizes and compositions from a minimum diameter of 4 nm. The independently calibrated GIV CNC-440 (modified N–P type counter) also agreed well with the N–P counters. The minimum size sensitivity of the N–P counter was examined showing a lower detection limit for insoluble (Ag) particles of around 2.6±0.3 nm diameter.

Black carbon in aerosol during BIBLE B

The Biomass Burning and Lightning Experiment (BIBLE) A and B campaigns over the tropical western Pacific during springtime deployed a Gulfstream‐II aircraft with systems to measure ozone and numerous precursor species. Aerosol measuring systems included a MASP optical particle counter, a condensation nucleus (CN) counter, and an absorption spectrometer for black carbon. Aerosol volume was very low in the middle and upper troposphere during both campaigns, and during BIBLE A, there was little aerosol enhancement in the boundary layer away from urban areas. In BIBLE B, there was marked aerosol enhancement in the lowest 3 km of the atmosphere. Mixing ratios of CN in cloud‐free conditions in the upper troposphere were in general higher than in the boundary layer, indicating new particle formation from gaseous precursors. High concentrations of black carbon were observed during BIBLE B, with mass loadings up to 40 μg m−3 representing as much as one quarter of total aerosol mass. Strong correlations with hydrocarbon enhancement allow the determination of a black carbon emission ratio for the fires at that time. Expressed as elemental carbon, it is about 0.5% of carbon dioxide and 6% of carbon monoxide emissions from the same fires, comparable to methane production, and greater than that of other hydrocarbons.

Turbulent mixing condensation nucleus counter

The construction and operating principles of the Turbulent Mixing Condensation Nucleus Counter (TM CNC) are described. Estimations based on the semiempirical theory of turbulent jets and the classical theory of nucleation and growth show the possibility of detecting particles as small as 2.5 nm without the interference of homogeneous nucleation. This conclusion was confirmed experimentally during the International Workshop on Intercomparison of Condensation Nuclei and Aerosol Particle Counters (Vienna, Austria). Number concentration, measured by the Turbulent Mixing CNC and other participating instruments, is found to be essentially equal.

The Effect of Boundary Conditions on Gas-phase Synthesised Silver Nanoparticles

We have prepared spherical non-agglomerated silver nanoparticles by an evaporation–condensation–dilution/cooling technique. Silver was evaporated from a crucible in a tubular flow reactor. A porous tube diluter was used to quench the carrier gas at the outlet of the reactor to enhance the formation of small particles and to suppress agglomeration and other particle growth mechanisms. The number size distribution of the prepared particles was measured with a differential mobility analyser–condensation nucleus counter combination and the size and the shape of the particles were analysed with transmission electron microscope. The system was modelled using a sectional aerosol dynamics computer code to estimate the importance of different aerosol processes. In all conditions the particles obtained were non-agglomerated and spherical. The mean particle diameter varied from 4 to 10-nm depending on boundary conditions. From the modelling studies it can be concluded that the nucleation rate is the most important parameter controlling the final particle size.

Measurement of aerosol sulfuric acid: 1. Experimental setup, characterization, and calibration of a novel mass spectrometric system

An instrument for the direct in situ measurement of aerosol sulfuric acid in the atmosphere has been developed, characterized and calibrated. The instrument termed Volatile Aerosol Component Analyzer (VACA) utilizes chemical ionization mass spectrometry technique for the detection of sulfuric acid. Prior to the mass spectrometric identification the sample flow is heated, and sulfuric acid is evaporated from the aerosol. The VACA system is characterized as a function of temperature, residence time in the flow reactor, aerosol size, and chemical composition. A unit consisting of an aerosol generator, a differential mobility analyzer, a hygrometer, and a condensation nuclei counter is used to calibrate the VACA instrument.

Sterilization by H 2O 2 droplets under corona discharge

A new sterilization method that combines an injection of hydrogen peroxide droplets (30 wt%) by spraying and a corona discharge is very effective for high-speed sterilization. Ultraviolet light, gaseous species and fine H 2O 2 droplets were considered to be important factors of this sterilization method. In order to investigate the sterilization mechanism, these three factors were examined. It was shown that ultraviolet light was not effective for sterilization. Among the gaseous species investigated, positive ions were proved to be effective through experiments using electric fields. A quadrupole mass spectrometer was used to measure positive ions. It was confirmed that H 2O 2 was decomposed and the number of H 2O 2 droplets was reduced. H 2O 2 droplet size was measured by a laser scattering method, CNC (condensation nuclei counter) and DMA (differential mobility analyzer). It was found that droplets larger than 3 nm still existed even if the droplet size was reduced. It was concluded that both fine H 2O 2 droplets and positive ions had important effects on sterilization.

Laboratory studies of the efficiency of selected organic aerosols as CCN

Experiments were conducted in the large (600 m 3) expansion chamber of the Calspan Corporation to test the efficiency of selected organic aerosols as cloud condensation nuclei (CCN). Solutions of pinonic acid (PA), ammonium sulfate (AS) (as a benchmark), and a mixture of both were nebulized and used for initial CCN spectra, as were products of cyclohexene and α-pinene oxidation by ozone. Measurements of the resulting aerosols were made with both particle-sizing instruments and a cloud condensation nucleus (CCN) counter. Activated cloud drop number concentrations (CDNC) were determined during chamber expansion by standard laser-scattering probes. The results support the contention that the presence of sparingly soluble organic components in aerosols significantly affect the rate at which these aerosols activate to form cloud drops. However, even the organic aerosols eventually fully activated to the extent expected due to size assuming complete solubility. It is only the time necessary to activate them which is altered and the atmospheric significance of this kinetic effect of organics is not yet clear.